The present invention relates to a fuel injection device for a single point injection type, and more particularly to an improved throttle body having a substantially horizontal suction passage therein and adapted to be horizontally connected to an intake manifold.
FIG. 11 shows a conventional throttle body of the above-mentioned type. Referring to FIG. 11, reference numeral 120 designates a throttle body constructed of an upstream body 122 having a suction passage 124 and a downstream body 126 having a throttle bore 128. The upstream body 122 is provided with a fuel injector 140 for injecting fuel into the throttle bore 128. A throttle valve 150 is fixed to a throttle shaft 152 rotatably mounted in the throttle bore 128.
The fuel injector 140 is so positioned as to inject fuel toward the throttle shaft 152 of the throttle valve 150, so that the fuel may be atomized in the throttle bore 128, and is distributed through the intake manifold into cylinders of an engine.
When the throttle valve 150 is rotated from its full closed position at a certain angle .theta..sub.1 as shown in FIG. 11, the fuel injected from the fuel injector 140 and colliding with the throttle shaft 152 is widely scattered downwardly onto an inner wall surface 128a of the throttle bore 128. As a portion of the throttle bore 128 upstream of the throttle valve 150 is under a substantially atmospheric pressure, and the throttle bore 128 is substantially horizontal, the fuel falling on the inner wall surface 128a of the throttle bore 128 is apt to stay on the inner wall surface 128a of the throttle bore 128, causing fluctuation of an air-fuel ratio when the opening angle of the throttle valve 150 is small at low- speed running or at idling, for example. Further, when the throttle valve 150 is opened from the small throttle angle position, the fuel staying in the throttle bore 128 tends to be sucked momentarily into the intake manifold to cause overrichness of the air-fuel ratio. As a result, the air-fuel ratio is widely fluctuated to adversely affect exhaust emission.